1. Field of the Invention:
The present invention relates to a narrow-band UV-B phototherapeutic device that is effective in the treatment of such conditions as psoriasis, atopic dermatitis, and leukoderma, and more particularly to the configuration of a light source that includes a fluorescent lamp, i.e., the ultraviolet light source for emitting narrow-band UV-B.
2. Description of the Related Art:
Ultraviolet light can be defined as electromagnetic waves within the range of wavelengths that includes as its upper limit wavelengths of 360–400 nm, which is shortest wavelengths of visible light and as its lower limit wavelengths of 1 nm. Ultraviolet light can be divided according to wavelength into a long wavelength band UV-A, a middle-wavelength band UV-B, and a short wavelength band UV-C. Ultraviolet light has a sterilizing effect and is known for its use in the treatment of skin disorders. In particular, ultraviolet light having an extremely narrow wavelength of 311±2 nm in the middle-wavelength band is referred to as narrow-band UV-B. This narrow-band UV-B has a therapeutic effect against psoriasis that surpasses that of UV-B (broadband UV-B) that includes other wavelengths and can achieve a therapeutic effect of the same level as UV-A. In addition, narrow-band UV-B has a lower carcinogenic effect than broadband UV-B or UV-A, and in contrast with treatment that employs UV-A, causes no constitutional symptom side effects such as nausea or disorders of the liver and gastrointestinal tract. The results of research to date have clearly shown that narrow-band UV-B has these excellent properties, and in recent years, treatments of skin disorders that use narrow-band UV-B have become common in many countries including the United States. Greater detail is provided in a paper by Akimichi Morita in “Clinical Dermatology,” Vol. 56, No. 5 (2002 Supplement) pages 106–111 (Apr. 10, 2002) published by Igaku Shoin.
Narrow-band UV-B phototherapeutic devices require an ultraviolet light source that emits ultraviolet light having a wavelength of 311±2 nm. As described in the above-described document, a fluorescent lamp (TL01) has been developed by Philips Holland as such an ultraviolet light source. This lamp is a straight-tube mercury-excited fluorescent ultraviolet lamp, and when used as the ultraviolet light source of a narrow-band UV-B phototherapeutic device, a plurality (10 in the example described in the above-referenced document) of lamps is arranged in parallel as the light source.
Typically, a phototherapeutic device requires that the intensity of the therapeutic light irradiated upon an affected area be uniform. This requirement arises due to the importance of avoiding a situation in which a particular area of affected areas that are simultaneously irradiated by light fails to receive the therapeutic effect due to insufficient irradiation, while other areas are subject to side effects due to excessive irradiation. This requirement is particularly important in a therapeutic device that uses light rays such as ultraviolet light having high energy.
Thus, in a narrow-band UV-B phototherapeutic device of the prior art that employs straight-tube ultraviolet fluorescent lamps, a plurality of fluorescent lamps are arranged in parallel within a plane to produce a planar light source in which the intensity of irradiated light is uniform. However, when the light source and treated area are close, it was impossible to avoid a situation in which the intensity of irradiation alternates regularly between strong and weak on the irradiated surface.
Distancing the light source from the treated area is a simple and effective method of dealing with this problem, and phototherapeutic devices of the prior art therefore normally irradiate the treated area from a distance. However, distancing the light source from the treated area also decreases the intensity of irradiation on the treated area. In particular, the UV-B ultraviolet light that is effective in the treatment of atopic dermatitis, psoriasis, and leukoderma is greatly attenuated in the air, and this attenuation drastically reduces the therapeutic effect and greatly extends the treatment time. Thus, the arrangement of a plurality of straight-tube fluorescent lamps was necessary to compensate for the reduction in the intensity of irradiation of the treated area in narrow-band UV-B phototherapeutic devices of the prior art. The intensity of emission of the light source was raised by using a plurality of fluorescent lamps.
For these reasons, a narrow-band UV-B phototherapeutic device of the prior art employing straight-tube fluorescent lamps could not avoid the necessity for a large light source and a lowered intensity of irradiation in the treated area. In addition, extra procedures such as masking areas other than the treated area were required to avoid the unnecessary exposure of healthy skin and the attendant serious, cancer-producing side effects. As a result, narrow-band UV-B phototherapeutic devices of the prior art have come to be mainly used in treatments that permit the extended treatment time that is necessary to compensate for the reduced intensity of irradiation of ultraviolet light and that also involve irradiation of ultraviolet light over a wide range, such as in the treatment of the entire body, the feet, the hands and the head. Even in such cases, however, patients must endure extended treatment time, the discomfort of remaining in the same position for an extended period of time during treatment, the inability to do anything else during treatment, and the great restrictions on daily routine.